Active matrix organic EL display device and manufacturing method thereof

ABSTRACT

An active matrix organic EL display device includes pixels each having an organic EL element ( 7   a ) and a pixel circuit ( 3 ) including a polysilicon TFT for controlling the organic EL element ( 7   a ) arranged adjacently in each of the regions partitioned into a matrix shape by data line ( 12 ) and gate line ( 11 ) that intersect each other. The organic EL element ( 7   a ) has a cathode ( 7 ) arranged in at least a region that excludes a space above the polysilicon TFT. The cathode ( 7 ) is arranged continuously over two or more adjacent pixels in the direction of gate line ( 11 ).

TECHNICAL FIELD

The present invention relates to an Organic Electro Luminescence (EL)display device and a manufacturing method thereof, and in particular, toan active matrix organic electro luminescence display device using apolysilicon Thin Film Transistor (TFT) as an active device and amanufacturing method thereof.

BACKGROUND ART

Liquid crystal display devices have generally been used for conventionallow-profile and light-weight flat-panel displays. The liquid crystaldisplay device has, however, a problem in that it has a smaller angle offield and poor response characteristics because it controls thetransmitted light with the orientation direction of the liquid crystal.Active matrix organic EL display devices have recently attractedattention which have a large angle of field and high responsecharacteristics. The organic EL element is a self-light-emitting elementbased on the principle in which the electric field applied can bring theholes injected from the anode and the electrons injected from thecathode into recombination, the energy of which can allow thefluorescent substance to emit light, thereby providing good visibility.The organic EL element also needs lower power consumption because nobacklight source is used, so that it is expected to become thealternative display device, particularly in hand-held device equipmentsuch as cellular phones.

The active matrix organic EL display device needs to increase thelight-emitting efficiency of the organic EL element itself by improvingthe injection efficiency of the holes in the light-emitting layer in thelaminated structure such as the hole injection layer/hole-transportlayer/light-emitting layer/electron-transport layer, and by improvingthe generation efficiency of excitons generated in the recombination andthe like. In order to improve the display quality in the active matrixorganic EL display device, the characteristic of the TFT needs to beimproved, such as the circuit response and the like.

In the above-mentioned TFT, amorphous silicon TFT that uses amorphoussilicon layer has mainly been used. The requirements for better TFTcharacteristics, however, have recently led to the development of TFTusing the polysilicon layer (hereinafter abbreviated as polysilicon TFT)with higher electric field mobility than the amorphous silicon layer.The manufacture of polysilicon TFT requires a process for thecrystallization of the amorphous silicon layer. Such a process includesa high-temperature process for crystallization at a temperature of about600° C. using an electric heating furnace, and a low-temperature processfor crystallization at a low temperature of about 300° C. or less usinglaser or infrared light.

High-temperature process has the advantages that the LSI (Large ScaleIntegration) technology can be used to form a thermally-oxidized gateinsulating layer and the TFT characteristic variation can be preventedbecause interface properties between the thermally-oxidized gateinsulating layer and the polysilicon are stabilized. Thehigh-temperature process, however, needs higher temperatures during theprocess of crystallization process, so that it cannot apply to displaydevices that use a substrate such as glass or plastic. Thelow-temperature process for crystallization using laser annealing orlamp annealing has thus usually been used for active matrix organic ELdisplay device.

A description is given below of an active matrix organic EL displaydevice with a polysilicon TFT made by the above-describedlow-temperature process (hereinafter referred to as a low temperaturepolysilicon TFT). FIG. 1A schematically shows a plan view of thestructure of the conventional active matrix organic EL display devicedescribed in Japanese application patent laid-open publication No.2001-318628. FIG. 1B shows a cross sectional view taken along the lineB-B′ in FIG. 1A. FIG. 2A to FIG. 2E, FIG. 3A to FIG. 3D, and FIG. 4A toFIG. 4C show process cross sectional views of a series of manufacturingprocedures for the active matrix substrate. FIG. 5 shows an equivalentcircuit diagram of the active matrix organic EL display device.

Referring first to FIG. 2A to FIG. 4C, a description is given of themanufacturing process of the active matrix substrate described in theabove-described reference. First, primary layer 101 is formed on glasssubstrate 100. Amorphous silicon is then deposited, and polysiliconlayer 102 is formed using laser annealing or lamp annealing or the like(see FIG. 2A). Next, on polysilicon layer 102 is formed protective layer103 of a silicon oxide layer, on which is formed resist mask 104. Usingresist mask 104, n-type impurities such as phosphorous or arsenic areadded to form n-type impurity region 105. The added impurities are thenactivated using laser annealing or the like (see FIG. 2B and FIG. 2C).Next, polysilicon layer 102 is locally removed to form island-shapedactive layers 106 to 109. Then, after gate insulating layer 110 has beenformed, gate electrodes 111 to 114, source wiring 115, andcurrent-supply line 116 are formed (see FIG. 2D and FIG. 2E).

Next, using gate electrodes 111 to 114 as masks, n-type impurities suchas phosphorous are doped in a self-alignment manner to form impurityregions 117 to 124. Then, using resist mask 125, n-type impurities suchas phosphorous are locally added to form impurity regions 126 to 130including a high concentration of phosphorous (see FIG. 3A and FIG. 3B).Next, using resist mask 131, p-type impurities such as boron are locallydoped to form impurity regions 132 to 135 including a high concentrationof boron (see FIG. 3C). Then, resist mask 131 is removed to provide acircuit element such as polysilicon TFTs (see FIG. 3D).

Next, first interlayer insulating layer 136 is formed on the circuitelement including polysilicon TFTs, and the impurity element isactivated with laser annealing or lamp annealing. Then, secondinterlayer insulating layer 137 is formed. Contact holes are then formedthrough first interlayer insulating layer 136, second interlayerinsulating layer 137, and gate insulating layer 110, down to theimpurity region. Then, metal is filled in each contact hole andpatterned to form wirings 138 to 145. Then pixel electrode 146 is formedin contact with connection electrode 141 (see FIG. 4A and FIG. 4B).

The above-mentioned processes in FIG. 2A to FIG. 4B are the same as thelow temperature polysilicon TFT manufacturing technology that is used inactive matrix liquid crystal display devices and the like. Theabove-mentioned processes can be achieved by applying technologies suchas polysilicon formation technology for forming polysilicon by formingand annealing the amorphous silicon layer, impurity implantationtechnology for forming n-type TFT and p-type TFT, conductive layerformation technology such as Al and insulating layer formationtechnology for layers of silicon oxide and silicon nitride, resist layerformation technology for defining these layer-formed regions andimplanted regions, and etching technology for removing regions that needno formed layer.

After pixel electrode 146 is formed, third interlayer insulating layer147 is formed as shown in FIG. 4C. The laminated structure included inthe organic EL element except for the anode and cathode has a thicknessas thin as about 80 nm to 200 nm, and the cathode has a thickness asthin as about 30 nm to 300 nm, so that steep shapes are covered beforeforming the organic EL element to prevent cracks from forming at thestep edges, and edges are tapered to prevent cracks at the edge steps.After the third interlayer insulating layer 147 is formed in a taperedshape, organic EL layer 148 is formed with vapor deposition technologyin the desired region in each pixel, and then, cathode 149 andprotective electrode 150 are formed. Finally, passivation layer 151 isformed to protect organic EL layer 148, thereby providing the activematrix organic EL display device.

As shown in the equivalent circuit in FIG. 5, the active matrix organicEL display device formed in the above-described manner has a pixelenclosed by gate wiring 145 disposed in a row direction, and sourcewiring 115 and current-supply line 116 disposed in a column direction.The pixel contains switching TFT 202 connected to gate wiring 145 andsource wiring 115, light-emitting element 204 including organic EL layer148 sandwiched between pixel electrode (anode) 146 and cathode 149 (seeFIG. 4C), and controlling TFT 203 including source and drain; one isconnected via holding capacitance 207 to the drain of switching TFT 202,and the other is connected to the anode of light-emitting element 204.Cathode 149 of light-emitting element 204 is common to all pixels. Inthis way, the cathode electrode may be a single electrode structureacross the entire display region, because wiring lines from the row andcolumn drivers can select the address for each pixel, so that cathode149 is only a power supply electrode.

As shown in FIG. 1A, on substrate 4001, the pixels represented in theabove-described equivalent circuit are arranged in a matrix to formpixel portion 4002, and gate-side drive circuit 4004 and source-sidedrive circuit 4003 are disposed along the ends in a row direction and acolumn direction. The above components are then sealed with firstsealing material 4101 and second sealing material 4104. Wiring 4005 as alead is formed during the sealing, and one end of FPC (flexible printcircuit) 4006 is connected to this wiring 4005. In the organic ELdisplay device thus obtained, as seen from FIG. 1B which shows the crosssection taken along the line B-B, in FIG. 1A (a connection with theoutside, a part of source-side drive circuit 4003, and a cross sectionof one pixel of pixel portion 4002), and as seen from FIG. 4C, thecathode electrode (which corresponds to cathode 149 and protectiveelectrode 150 in FIG. 4C, and cathode 4305 in FIG. 1B) is formed acrossthe entire display region where pixels are arranged in a matrix, andthus also formed over pixel circuits including polysilicon TFTs, andover wiring lines connecting the row and column drivers to the pixelcircuit.

There are two problems as follows with respect to the structure of theconventional active matrix organic EL display device in which thecathode electrode that constitutes a part of the organic EL elements isformed across the entire display region as a single electrode.

The first problem is that because the cathode electrode is formed acrossthe entire display region and thus also formed over wiring linesconnecting the row and column drivers to the pixel circuits, capacitancearises between this wiring line and the cathode electrode, which delaysthe signals traveling on the wiring line. Such delayed signals may limitthe frame frequency, which makes it difficult to provide an activematrix organic EL display device that is adaptable to high-speed movingvideo pictures. Sending signals to the wiring line that has theabove-described capacitance is also disadvantageous in terms of powerconsumption and may prevent lower power consumption from being achieved.

The second problem is that in the vapor deposition process for formingthe cathode electrode, the electron beam vapor deposition source cannotbe used as a vapor deposition source. This problem is described morespecifically below.

The vapor deposition process is a technology that heats and evaporatesmaterials that are to be coated in a vacuum and deposits them on asubstrate. While there are many methods for heating the materials to becoated, the electron beam vapor deposition source is often used forgeneral mass production. This is because, compared to other vapordeposition sources, the electron beam vapor deposition source has a morestable evaporation angle for the materials to be coated which canprovide a higher quality vapor deposition layer, and it provides lesssprats and more uniform layers, and allows for easier filling of thematerials to be coated, and needs less maintenance, which can increasethe capacity utilization of the film formation facility.

It has become apparent, however, that when the cathode electrode of theconventional active matrix organic EL display device is formed with thevapor deposition system including the electron beam vapor depositionsource, the cathode electrode is formed across the entire display regionand thus also formed over the polysilicon TFTs, so that thecharacteristic X-ray emerging from the electron beam vapor depositionsource may degrade the polysilicon TFT characteristics, by changing thethreshold voltage Vt, increasing the leak current, decreasing theon-state current and the like.

FIG. 6 shows experimental results of the characteristic change ofpolysilicon TFTs which are irradiated with X-ray. In FIG. 6, the x-axisshows the gate voltage, and the y-axis shows the drain current. As seenin FIG. 6, X-ray exposure can shift the polysilicon TFT characteristicsto the more negative value (to the left in the drawing) for both thepch-TFT and nch-TFT. This gate voltage shift may prevent the normal TFToperation, and make it impossible to realize a high image qualitydisplay device without lines or non-uniformity on the screen.

The above-described gate voltage variation of the polysilicon TFTs mayarise from the trap levels generated in the gate insulating layer of thepolysilicon TFTs. Each of the TFTs arranged in matrix, in conventionalpolysilicon TFT, particularly the polysilicon TFT made with thelow-temperature process, however, lacks sufficient characteristics anduniformity, which makes it impossible to demonstrate the effect of thecharacteristic X-ray. The inventors of the present invention havedemonstrated the effect of the characteristic X-ray by improving the lowtemperature polysilicon TFT manufacturing technology to make it possibleto manufacture the polysilicon TFT with good characteristics and gooduniformity thereof. The novel fact that the inventors of the presentinvention have found is the detailed relationship between thecharacteristics X-ray from the electron beam vapor deposition and thegate voltage variation of the low temperature polysilicon TFT.

As described above, the conventional active matrix organic EL displaydevice has a cathode electrode that is formed across the entire displayregion and thus also formed over the wiring lines connecting the row andcolumn drivers to the pixel circuit and over the polysilicon TFTs. Thismay cause a signal delay problem due to capacitance arising between thewiring lines and cathode electrode, and the polysilicon TFTcharacteristic degradation problem due to the characteristic X-ray thatare generated during the electron beam vapor deposition, thus making itimpossible to realize a high-speed-response and high-quality displaydevice.

The present invention was realized in light of the above-describedproblems, and aims mainly to provide an active matrix organic EL displaydevice and a manufacturing method thereof which can prevent, withoutcomplexing the manufacturing process, the display quality decreasecaused by the signal delay that occurs due to the capacitance betweenthe wiring lines and cathode electrode and the polysilicon TFTcharacteristic degradation.

DISCLOSURE OF INVENTION

To realize the above-described object, the active matrix organic ELdisplay device according to the present invention is an active matrixorganic EL display device including a pixel that has an organic ELelement and a polysilicon TFT for controlling the organic EL elementwhich are disposed adjacent to each other, the pixel being formed ineach of the regions partitioned into a matrix by a plurality ofintersecting data lines and scanning lines, wherein the organic ELelement has a cathode electrode provided in at least a region excludinga region over said polysilicon TFTs.

In the above-described device, the cathode electrode may be providedcontinuously over two or more adjacent pixels in a direction of the dataline or scanning line.

The organic EL element may include a light-emitting region, and thecathode electrode may be formed to enclose or to cover thelight-emitting regions of the two or more adjacent pixels.

The cathode electrode may be provided in a region which excludes theregion over the polysilicon TFT and excludes a region over one wiringline of the data line and scanning line that partitions the pixelregions.

In addition, the cathode electrode may be provided continuously over twoor more adjacent pixels in the direction of the one of said wiringlines.

In addition, the organic EL element may include a light-emitting region,and the cathode electrode may be formed to enclose or cover thelight-emitting regions of the two or more adjacent pixels.

Another active matrix organic EL display device according to the presentinvention is an active matrix organic EL display device including apixel that has an organic EL element, the pixel being formed in each ofthe regions that are partitioned into a matrix by a plurality ofintersecting data lines and scanning lines, wherein the organic ELelement has a cathode electrode which is provided in at least a regionexcluding a region over one wiring line of the data line and scanningline partitioning the pixel regions and provided continuously over twoor more adjacent pixels in the direction of the one wiring line.

In the above-described device, the organic EL element may include alight-emitting region, and the cathode electrode may be formed toenclose or cover the light-emitting regions of the two or more adjacentpixels.

In any one of the above-mentioned inventions, the area between oppositeedges of the region where the cathode electrode is formed and the regionwhere the polysilicon TFT is formed may be 20 μm or more.

The area between opposite edges of the region where the cathodeelectrode is formed and the region where the one wiring line is formedmay be 20 μm or more.

In addition, the cathode electrode that is provided continuously overtwo or more adjacent pixels may be formed in a strip, the active matrixorganic EL display device may further include at least one cathodeelectrode wiring which extends in the direction of the narrow area ofthe cathode electrode, and the cathode electrodes in strips may bearranged along the cathode electrode wiring and each of the cathodeelectrodes may be connected to the cathode electrode wiring.

In addition, the cathode electrode may comprise a vapor deposition layerincluding lithium or a lithium compound and aluminum.

A method for manufacturing an active matrix organic EL display deviceaccording to the present invention is a method for manufacturing anactive matrix organic EL display device including a pixel that has anorganic EL element and a polysilicon TFT for controlling the organic ELelement which are disposed adjacent to each other, the pixel beingformed in each of the regions that are partitioned into a matrix by aplurality of intersecting data and scanning lines, comprising the stepof forming the polysilicon TFT on a substrate, and forming a cathodeelectrode of the organic EL element on the substrate with electron beamvapor deposition using a vapor deposition mask covering at least aregion where the polysilicon TFT is formed.

In the above-described method, the cathode electrode may be formed in astrip to be provided continuously over two or more adjacent pixels inthe direction of the data line or scanning line.

The organic EL element may include a light-emitting region, and thecathode electrode may be formed to enclose or cover the light-emittingregions of the two or more adjacent pixels.

In addition, before forming the polysilicon TFT, at least one cathodeelectrode wiring which extends in the direction of the narrow area ofthe cathode electrode may be formed on the substrate, and in forming thecathode electrode in a strip, each of the cathode electrodes formed instrips may be connected to the cathode electrode wiring through contactholes.

The cathode electrodes may be formed with material including lithium ora lithium compound and aluminum.

In the above-described active matrix organic EL display device andmanufacturing method thereof according to the present invention, thecathode electrode is not formed over the polysilicon-TFT-formed regionincluded in the pixel circuit. This configuration can protect thepolysilicon TFT via the vapor deposition mask in the vapor depositionprocess to prevent the polysilicon TFT characteristic degradation due tothe X-ray. This allows use of the electron beam vapor deposition systemin high mass production capability to realize high image quality displaydevices without lines or nonuniformity on the screen, having controlcircuits comprised of polysilicon TFTs that have less characteristicvariation and perform according to design specification.

In the present invention, the cathode electrode formed by the vapordeposition process is not formed over the wiring lines (data line andscanning line) that connects the row driver and column driver to thepixel circuits. This configuration can reduce the capacitance betweenthe wiring lines and cathode electrodes so that the driver can operateat lower power and high-speed. This allows a higher frame frequency andthus enables a display device that has less flicker and is adaptable tothe high-speed animation.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1A shows a plan view of the structure of the conventional activematrix organic EL display device.

FIG. 1B shows a cross sectional view taken along the line B-B′ in FIG.1A.

FIG. 2A to FIG. 2E show cross sectional views of manufacturingprocedures for the conventional active matrix organic EL displaydevices.

FIG. 3A to FIG. 3D show cross sectional views of manufacturingprocedures for the conventional active matrix organic EL displaydevices.

FIG. 4A to FIG. 4C show cross sectional views of manufacturingprocedures for the conventional active matrix organic EL displaydevices.

FIG. 5 shows an equivalent circuit diagram of the conventional activematrix organic EL display device.

FIG. 6 illustrates the problem with the conventional active matrixorganic EL display device, showing TFT gate voltage change due to theX-ray exposure.

FIG. 7A schematically shows a block diagram of the configuration of theactive matrix organic EL display device according to the first exampleof the present invention.

FIG. 7B shows the configuration of one pixel of the active matrixorganic EL display device shown in FIG. 7A.

FIG. 8 shows a plan view of the structure of the active matrix organicEL display device according to the first example of the presentinvention.

FIGS. 9A and 9B show cross sectional views of portions of themanufacturing process of the active matrix organic EL display deviceaccording to the first example of the present invention.

FIG. 10 shows a plan view of the structure of the active matrix organicEL display device according to the second example of the presentinvention.

BEST MODE FOR CARRYING OUT THE INVENTION

The preferred embodiments of the present invention will now be describedin more detail below with reference to the accompanying drawings.

The active matrix organic EL display device according to one embodimentof the present invention includes, on a glass substrate, organic ELelements arranged in a matrix, pixel circuits including polysilicon TFTfor controlling each organic EL element, and a row driver and a columndriver for controlling the pixel circuits, wherein cathode electrodesare formed, using the vapor deposition mask having a metal plate with anopening formed thereon and the electron beam vapor deposition source, inregions which exclude regions over the polysilicon TFTs or regions overthe polysilicon TFTs and scanning line wirings, to enclose thelight-emitting portions of two or more successive pixels in the scanningline wiring direction. The cathode electrodes are not formed over thewiring lines which connect the row drivers or column drivers to thepixel circuits and the scanning line wirings in order to reduce thecapacitance between the wiring line and cathode electrode, and the vapordeposition mask covers the polysilicon TFTs while forming the cathodeelectrode so as to make it possible to prevent the TFT characteristicdegradation due to the X-ray from the electron beam vapor depositionsource.

Embodiments of the present invention will be described in detail belowwith reference to examples 1 and 2.

Example 1

A description is given of the configuration and the manufacturing methodof the active matrix organic EL display device according to the firstexample of the present invention. FIG. 7A shows the configuration of theactive matrix organic EL display device according to the first exampleof the present invention and is a block diagram that includes the entiredisplay region. FIG. 7B shows a partial enlarged view of one pixel(sub-pixel) in FIG. 7A. FIG. 8 shows a plan view of the structure of theactive matrix organic EL display device according to the first exampleof the present invention, and FIG. 9A and FIG. 9B illustrate portions ofthe manufacturing process thereof and are cross sectional views takenalong the line A-A′ in FIG. 8.

In the following account, the description is omitted to simplify theexplanation of items such as a sealing structure for preventingdegradation of the organic EL element and the manufacturing processrelated to the sealing, an electrical connection structure including FPC(flexible print circuit) which connects the glass substrate (hereinafterreferred to as a display substrate) including the polysilicon TFTs andorganic EL elements to the external power supply, and the manufacturingprocess thereof, and a circuit for supplying power and inputting signalsto the display substrate.

As shown in FIGS. 7A and 7B, the active matrix organic EL display devicein this example has organic EL element 7 a formed in each sub-pixelwhich corresponds to each of the RGB primaries included in one pixel.Organic EL elements 7 a are arranged in a transversal (row) directionand have a rectangular shape in the up-down direction of the drawingfigure. As shown, each sub-pixel includes organic EL element 7 a overwhich pixel circuit 3 is provided for controlling organic EL element 7a. The pixels as configured above are arranged in a matrix to form adisplay region, which has row drivers 1 a disposed on its right and leftsides for selecting rows. The display region has thereunder columndriver 2 a for controlling the brightness of each sub-pixel. Row driver1 a and column driver 2 a select a pixel and the selected pixels eachemits light with controlled brightness to act as the display.

Each sub-pixel has cathode electrode 7 for the organic EL element whichis formed independently for each row. As shown in FIG. 8, cathodeelectrode 7 is not formed over pixel circuit 3 includingpolysilicon-formed region 10 a, but is formed over organic EL elementlight-emitting regions 5 which are included in each of two or moresuccessive pixels in the wiring direction of row driver 1 a, and overthe wiring of column driver 2 a disposed between light-emitting regions5. Cathode electrode 7 is electrically connected through contact hole 6on cathode electrode wiring 4 between the display region androw-driver-formed region. The wiring line from row driver 1 a to pixelcircuit 3 and cathode electrode wiring 7 include multilevelinterconnection structures which are certainly electrically independent.

Structures shown in FIGS. 7A, 7B, and 8 are examples, and arrangementssuch as for organic EL element light-emitting region 5 and pixel circuit3 in each pixel, sub-pixels for the RGB primaries, row driver 1 a,column driver 2 a, and cathode electrode wiring 4, can be optionally setfor different designs. Cathode electrode 7 and cathode electrode wiring4 may be connected on one side or two opposite sides of each of thepixels (i.e., three adjacent sub-pixels).

Referring now to process cross sectional views in FIGS. 8, 9A, and 9B, adescription is made of the manufacturing process for the active matrixorganic EL display device as configured above.

As shown in FIG. 9A, the display substrate of the active matrix organicEL display device of this example has thereon pixel circuit 3 includingpolysilicon TFTs formed with the low temperature polysilicon TFTmanufacturing technology and other elements, and various wiring linessuch as gate line 11, data line 12, power supply line 8, and cathodeelectrode wiring 4.

Pixel circuit 3 can be formed with polysilicon layer formationtechnology in which the amorphous silicon is crystallized with laser orlamp annealing, and deposition, patterning, and etching technologieswhich are well known in semiconductor manufacturing technology, andother technologies. More specifically, pixel circuit 3 is formed asfollows. First, an insulating layer such as silicon oxide layer isformed on a translucent substrate such as glass with CVD, on whichamorphous silicon is deposited. Subsequently, impurity doping andpolysilicon-forming processes such as laser annealing are performed.Then, resist coating, exposure and etching processes are performed inorder to form polysilicon 10 in the TFT-formed region. Next, the gateinsulating layer including layers such as the silicon oxide layer, andWSi (tungsten silicide) and the like are sequentially deposited, PR(photoresist) coating and etching are also performed in order to formthe gate electrode and gate wiring 11, and then the impurity doping isperformed in order to form the polysilicon TFT. Then, CVD is used todeposit an interlayer insulating layer including a silicon oxide layer,and PR coating and etching are performed to form contact holes, on whichAl and the like are deposited, PR coating and etching are performed toform source/drain electrodes, data line 12, power supply line 8, cathodeelectrode wiring 4 and the like.

Before forming polysilicon TFT on the substrate, WSi and metal and thelike may be deposited as an underlying layer of the TFT-formed region toform a light blocking layer. In the structure example shown in FIG. 9A,gate line (scanning line) 11 and wiring lines such as data line 12 andcathode electrode wiring 4 are laminated via the interlayer insulatinglayer (insulating layer 9 a). Alternatively, as with the conventionaltechnologies shown in FIGS. 1 and 2, these wiring lines may be formed onthe same layer and the intersections may be connected with bridges.

In this way, the polysilicon TFTs and various wiring lines are formed onthe substrate, on which the ITO (Indium-Tin Oxide) electrode for anode13 of each organic EL element 7 a is formed, then insulating layer 9 b,in which organic EL element light-emitting region 5 is opened and edgesof the opening are tapered, is formed with oxide layer formationtechnology such as CVD and isotropic etching technology, oredge-rounding technology in which the photosensitive resist is cured. Inthis example, cathode electrode 7 is separately formed for each pixel,so that contact holes 6 are formed at the same time for connecting eachcathode electrode 7 with cathode electrode wiring 4. The edge of thiscontact hole 6 is also tapered to prevent cracks in cathode electrode 7from forming at the step edges. Then, the hole-injection layer,hole-transport layer, light-emitting layer, and electron-transportlayer, which are known as the organic EL element structure, are seriallyformed by vapor deposition technology and the like to create organiclayer 14. This organic layer 14 may be any structure of thehole-transport layer/light-emitting layer/electron-transport layer,hole-transport layer/light-emitting layer/electron-transportlayer/electron-injection layer, or just the light-emitting layer. Forthe matrix color display, light-emitting layers made up of differentmaterials are laminated for each pixel.

Next, as shown in FIG. 9B, cathode electrode 7 made of Li or a Licompound and Al, for example, is formed with vapor depositiontechnology. In the conventional active matrix organic EL display device,cathode electrode 7 (cathode 4305 in FIG. 1, cathode 149 and protectiveelectrode 150 in FIG. 4) is formed across the entire display region, sothat problems arise in which the capacitance between cathode electrode 7and the wiring line that connects row driver 1 a and column driver 2 ato pixel circuit 3 may delay signals and thus degrade the responsecharacteristics, and X-ray during the electron beam vapor deposition maydegrade the polysilicon TFT characteristics. In this example, to solvethese problems at the same time, cathode electrode 7 is not formedacross the entire display region, but is formed, as shown in FIG. 8, ina region apart from pixel circuit 3 including the polysilicon TFT andconnection wiring at a predetermined distance (more specifically, aregion apart from polysilicon-formed region 10 a by L1). In doing so,pixel circuit 3 needs to be covered up so as not to form cathodeelectrode 7 over pixel circuit 3. Organic layer 14 is formed, however,under cathode electrode 7, so that the resist pattern cannot be used toselectively form cathode electrode 7. In this example, cathode electrode7 is formed using a vapor deposition mask made from a metal plate suchas Inver with wet etching technology. More specifically, on thesubstrate is positioned the vapor deposition mask, on which isdeposited, for example, Li or a Li compound and Al (e.g., co-depositionof lithium 0.1 wt % aluminum) with a layer thickness of about 500 nm. Inthis way, the vapor deposition mask is used to form cathode electrode 7.The pattern of cathode electrode 7 is, for the configuration as shown inFIG. 8, a strip shape that includes EL element light-emitting region 5and each contact hole 6 on cathode electrode wiring 4 for each row (eachsub-pixel for the RGB primaries). Cathode electrode 7 is alsoelectrically connected to cathode electrode wiring 4 via each contacthole 6. Then, the protective electrode and passivation layer are formed,if necessary, to complete the display substrate.

The above-described vapor deposition mask is used to protect pixelcircuit 3 including the polysilicon TFTs and connection wirings toprevent capacitance between cathode electrode 7 and connection wirings,as well as to eliminate the possibility of the polysilicon TFTcharacteristic degradation due to X-ray, so that the vapor depositionprocess for forming cathode electrode 7 can use the electron beam vapordeposition source to provide a high quality vapor deposition layer,thereby making it possible to improve the organic EL elementcharacteristic uniformity and mass production capability. It ispreferable that the vapor deposition mask usually has a thickness ofabout 50 μm to maintain enough strength. Such a range of metal layerthickness can sufficiently absorb X-ray that emerges from the electronbeam vapor deposition source.

In the active matrix organic EL display device formed as describedabove, any one pixel selected by the scanning line wiring andcolumn-side wiring receives a voltage on its organic EL layer throughanode 13 from power supply line 8 and through cathode electrode 7 fromcathode electrode wiring 4. This allows any organic EL element to emitlight at a desired brightness, thereby functioning as the displaydevice.

The example in FIG. 8 shows cathode electrode 7 that is formed at thedesigned position, and the same distances (L1 and L2) are assumedbetween polysilicon-formed region 10 a and cathode electrode 7. Whenmanufacturing the actual display device, misalignment may occur betweenthe cathode-electrode-formed region and polysilicon-formed region 10 aon the glass substrate. The distances (L1 and L2) betweenpolysilicon-formed region 10 a and cathode electrode 7 thus need to beset to prevent misalignment from overlapping cathode electrode 7 andpolysilicon-formed region 10 a on a plane. In view of the current vapordeposition technology that may cause about 20 μm of the above-describedmisalignment, the distances (L1 and L2) are preferably set at 20 μm ormore between polysilicon-formed region 10 a and cathode electrode 7.

Example 2

The active matrix organic EL display device according to the secondexample of the present invention and manufacturing method thereof willnow be described. FIG. 10 shows a plan view of the structure of theactive matrix organic EL display device according to the second exampleof the present invention.

In the above-mentioned first example, cathode electrode 7 is formed soas not to overlap with pixel circuit 3. Cathode electrode 7 ispreferably formed not to overlap with the wiring line as much aspossible in order to further reduce capacitance between the wiring lineand cathode electrode 7. In this example, cathode electrode 7 is formedin a region that does not overlap with either polysilicon-formed region10 a or the scanning line wiring (gate wiring 11).

The manufacturing method of the active matrix organic EL display devicein this example, which is basically the same as with the above-mentionedfirst example, forms, for each row, cathode electrode 7 in a strip toinclude organic EL element light-emitting region 5 and contact holes 6on cathode electrode wiring 4. Again, vapor deposition mask is used toform cathode electrode 7 of Li or a Li compound and Al with electronbeam vapor deposition. The distance (L1) between polysilicon-formedregion 10 a and cathode electrode 7, and the distance (L3) between thescanning line wiring (gate wiring 11) and cathode electrode 7 are alsopreferably set at 20 μm or more in view of the misalignment.

Also in this example, the vapor deposition mask that protects thepolysilicon TFT can prevent polysilicon TFT characteristic degradationduring electron beam vapor deposition. The electron beam vapordeposition source can thus be used to provide a high quality vapordeposition layer that improves the organic EL element characteristicuniformity and mass production capability. In addition, since cathodeelectrode 7 is formed in a region the position of which is shifted fromthe scanning, line wiring (gate wiring 11) to the pixel side, it maycreate smaller organic EL light-emitting region 5 than in the firstexample, but can provide lower capacitance between cathode electrode 7and the scanning line wiring, which makes possible a higher-speedoperation.

In each example described above, organic EL light-emitting region 5 andpixel circuit 3 are arranged in the same manner in each pixel so thatcathode electrode 7 is formed in a simple strip, but the presentinvention is not limited to such a shape. Cathode electrode 7 may be anyshape that does not overlap with pixel circuit 3 including thepolysilicon TFTs or the scanning line wirings such as gate line 11. Thevapor deposition mask is, unlike the photomask, difficult to form withprecise dimensions and difficult to align, so that it is preferably assimple a shape as possible. The layout of the vapor deposition mask isarranged so that the shape thereof becomes in view of the arrangement ofpixel circuit 3 and arrangement direction of the pixels and the like.

The above-described active matrix organic EL display device according tothe present invention and manufacturing method thereof can provide thefollowing effects.

The first effect is that a high image quality display device withoutlines or non-uniformity on the screen can be achieved because the activematrix organic EL display device includes the control circuit includinga polysilicon TFT that has less characteristic variation and performsaccording to specification. This is because the cathode electrode formedwith the vapor deposition process is not formed over thepolysilicon-TFT-formed region. That is, the vapor deposition maskprotects the polysilicon TFTs during the vapor deposition process, sothat the electron beam vapor deposition source, which may expose thesubstrate to X-ray, will not affect the various characteristics of thepolysilicon TFT, thereby allowing for the display image quality that isderived from the design characteristics.

The second effect is that a higher frame frequency can be set to providea display device that has less flicker and is adaptable to high-speedmoving video pictures. This is because the cathode electrodes are notformed over the wiring lines which connect the row drivers or columndrivers to the pixel circuits and the scanning line wirings in order toreduce the capacitance between these wiring lines and cathode electrode.Accordingly, a higher frame frequency can be set to provide a displaydevice that has less flicker and is adaptable to high-speed moving videopictures. The reduced capacitance allows the driver to operate at lowerpower which can provide the display device with lower power consumption.

1. A method for manufacturing an active matrix organic EL display deviceincluding a pixel that has an organic EL element and a polysilicon TFTfor controlling said organic EL element which are disposed adjacent toeach other, the pixel being formed in each of regions partitioned into amatrix by a plurality of intersecting data lines and scanning lines,comprising the steps of: forming on said substrate at least one cathodeelectrode wiring, then forming said polysilicon TFT on a substrate, andforming a cathode electrode of said organic EL element in a strip to beprovided continuously over two or more adjacent pixels in a direction ofsaid data line or scanning line, the position of which is opposite theside where said polysilicon TFT is connected, on said substrate withelectron beam vapor deposition using a vapor deposition mask covering atleast a region where said polysilicon TFT is formed, wherein saidcathode electrode wiring extends in a direction of the narrow area ofthe cathode electrode, and in forming said cathode electrode in thestrip, connecting each of said cathode electrodes formed in strips tosaid cathode electrode wiring through contact holes.
 2. The method formanufacturing an active matrix organic EL display device according toclaim 1, wherein said organic EL element includes a light-emittingregion, further comprising the step of forming said cathode electrode tocover said light-emitting regions of said two or more adjacent pixels.3. The method for manufacturing an active matrix organic EL displaydevice according to claim 1, further comprising the step of forming saidcathode electrode with material including lithium or a lithium compoundand aluminum.